Electronic digital cameras are superseding traditional cameras which rely upon chemical processing. As with other consumer oriented electronic products there is great pressure to reduce costs. There is also the need for low cost solid state image sensors to complement computers and communication devices and for practicable video conferencing and so on. The image input device is central to such applications. CMOS image sensors have proven themselves to be superior image input devices for low power mobile operations. CMOS image sensors may also have other applications. An important advantage of CMOS image sensors (or imagers) is that imager and signal processing circuits can easily be integrated on a single semiconductor chip. This brings into prospect single-chip camera systems. Charge coupled devices (CCDs) are used as an alternative to CMOS imagers, however, the latter may be cheaper to fabricate for a given level of performance and capacity. CMOS fabs such as may be used to build the invention are well known in the art. Typically, image sensors produce digitized raster-like arrays of electronic luminance signals corresponding to and responsive to the incident light that makes up an image.
The image sensor quality produced by CMOS image sensors has been improving in recent years to the point that CMOS image sensor performance begins to rival CCD image sensor performance. Thus, CMOS image sensors have begun to penetrate the DSC (digital still camera) marketplace. In order to ensure good image quality, CMOS image sensors may use CDS (correlated double sampling) circuits to remove FPN (fixed pattern noise). CDS is well known in the art. The use of CDS circuits has introduced a problem in that pictures of extremely bright lights or reflections from shiny surfaces may be imaged poorly. In these conditions, a spurious dark central area may appear in the middle of a very bright area. This phenomenon is sometimes termed image inversion. A method and image sensor with over-saturation detection and image inversion correction circuitry that solves the subject problem is described.